1. Technical Field
The present invention relates to a light source device, a method of driving a discharge lamp, and a projector.
2. Related Art
As a light source of a projector, a discharge lamp such as a high pressure mercury lamp and a metal halide lamp is used. As a method of driving such a discharge lamp, for example, there is a method of supplying a high frequency alternating current as a driving current to an antenna in a discharge lamp body (see JP-A-2007-115534). According to the method of driving the discharge lamp, it is possible to obtain stability of discharge, it is possible to prevent blackening or devitrification of the discharge lamp body from occurring, and thus it is possible to suppress decrease of durability of the discharge lamp.
However, for example, when the high frequency alternating current is supplied to an pair of electrodes arranged to be opposed in the discharge lamp body in which a discharge medium is enclosed, to turn on the discharge lamp, using the method of driving the discharge lamp in JP-A-2007-115534, arc discharge occurs between the pair of electrodes, the electrodes are at high temperature, the electrodes are partially melted, a space between the electrodes is broaden.
For example, in the usage for a projector, to improve efficiency in light usage, it is preferable to keep a narrow state between the electrodes, and intensity of light emission is small. It is not preferable that the space between the electrodes is broadened from each other during ignition, since the efficiency of light usage is decreased. The change between the electrodes means change in impedance between the electrodes. For this reason, even when the discharge lamp is efficiently turned on at the initial time of ignition, impedance mismatching occurs as the time elapses. As a result, there is a problem that reactive power is increased, and the efficiency is decreased.
Meanwhile, there is a driving method of supplying an alternating current (a direct alternating current) with a rectangular waveform as a driving current (for example, see JP-A-2010-114064). According to the method of driving the discharge lamp of JP-A-2010-114064), even when the protrusions of the front end portions of a pair of electrodes are temporarily melted by discharge, the protrusions are formed again during the discharge, and thus it is possible to keep the state where the electrodes are narrow.
However, in the driving method disclosed in JP-A-2010-114064, blackening or devitrification of the discharge lamp body occurs, and durability of the discharge lamp may be decreased.